73 MFI running way too rich

[caproader]

Guys,

After a run to the local Saturday car guys coffee event, the 73 sporto S spun wonderfully, but refused to fire. When I took the plugs out, they were all very black and very wet. Short term, the solution was to run home to get the back up plugs. When I got them installed, the car ran great.

So now the challenge is to figure out how to fix the problem. The car only has 55k miles in 36 years so I figure the inside of the MFI pump has got to look like the black jello I spooned out of the brake system when I got the car.

Not having taken an MFI pump apart, would the first step be to run a couple cans of something like Techron through the system or is this a case of 'go directly to taking the thing apart and clean it'? If so, I have a spare pump to practice on, but I need some direction. Is there an article somewhere or a maintenance thread that I can print out. Or is there a middle ground of doing some other sort of adjustment?

All help greatly and humbly appreciated.

John
73 Sporto S and 73 2.7 MFI

[orange911]

Follow the CMA - Check Measure and Adjust. It may be as simple as your thermostat is sticking or the cold start is not resetting. READ, READ, READ all of the information on Pelican and here. Please do not adjust anything until you have learned the system. Throttle bodies should be looked into for carbon build up on the air bypass screws if the other 2 items check out ok.

[edmayo]

Hi john, adding to what Olin said about not adjusting anything yet, which is very good advice, a quick initial check is to see whether the thermostat is getting the proper amount of heat. Since the car must have started initially and evidently ran well enough to get to coffee and home again, albeit with another set of plugs, we can assume to some extent that most everything is working. Start it and drive until the oil is up to operating temp. Now put your hand on the thermostat housing, it should be hot enough to not want to leave your hand on it for long. If not then your heater hose to the heat exchanger may be broken or the hot air hoses from the exchanger to the thermostat are broken. If the thermostat housing IS hot then the first step would be to CAREFULLY remove, dissassemble and clean the bimetallic discs in the thermostat. There are shims on the end of the thermostat closest to the removeable end cap, you must get those back in in the correct position. BE VERY CAREFUL ON dissassembly to lay out everything in order. Also be aware that the thermostat hoses from the engine side pan to the thermostat housing are actually two hoses, an inner and outer to insulate the heat in so it gets to the thermostat. Nothing wrong with Techron idea either.

[caproader]

Olin and Ed:

Thanks for the thoughts. Just after I got the car, I took the engine out to clean off all the external crud and replace the engine compartment insulation pad. When I had the engine out, I made sure that the pre-heater hoses were all attached and working correctly. Looks like now it is time to get out the manual and my spare pump and learn how to do some internal cleaning.

However, there will be a short pause in the action while Mark Peebles and I compete in One Lap of America starting on Friday with the 73 2.7 MFI car.

John
OMARC Racing
Old man's Automobile Club Racing

[72targa]

Don't over do it with Techron. Read the label. Probably no more than 2 bottles per oil change. You run the risk of thinning out your engine oil. Please don't run your engine with too light of a viscosity of oil.

[cmcfaul]

By far the easiest way to lean it out is to simply adjust the linkage to the MFI pump. Back it out a couple turns and see what happens. Keep track of the number of turns so you can put it back exactly as it was.

Chris
73 911 E

[orange911]

By far the easiest way to lean it out is to simply adjust the linkage to the MFI pump. Back it out a couple turns and see what happens. Keep track of the number of turns so you can put it back exactly as it was.

Chris
73 911 E

As noted above about using caution when adjusting. Most of the times this is just band-aiding another problem. Find the problem before adjusting. I know you want to drive it leaner, but you don't want to mask other issues when doing the CMA.

[304065]

Yes, adjusting the pump link away from 114mm is a bad idea, it throws the fuel curve off.

Any competent porsche driver tracks faster if brakes come smoothly

air filter
compression loss
plugs
dwell
timing (ignition timing)
fuel pressure
injectors (clean and verify spray pattern)
belt (injection pump timing)
correlation (VERY important)
smog (AFR or CO)

Never deviate from this sequence.

I would add a couple things before starting CMA, which should be obvious but bear repeating-- check to make sure all the parts of the MFI system are present and not damaged. For example, you should have two paper hoses, an inner and an outer, running from the port-side engine tin to the thermostat housing. If you don't feel HOT air escaping from the thermostat housing exhaust, go back up the chain until you find the problem. Often the paper hoses have been replaced with something else, mice get in, etc. Or the rubber "steam" hose between the heat exchanger and the engine tin has been severed or removed. Obviously the lack of thermostat warmup will cause the engine to run at about 10:1 AFR.

[caproader]

John,

As always, thanks to every one for the good advice. It appears that everything is attached in good working order; including the inner and outer hose from the left side tin to the pump and the thicker hose from the left side heat exchanger to the left side tin. All parts seem to be present or accounted for. I'm afraid that the problem might be associated with only an average of 1500 miles a year and/or a long time sitting with bad gas in the pump.

John

[Mr9146]

By far the easiest way to lean it out is to simply adjust the linkage to the MFI pump.

Wow! That's some DANGEROUS advice.